The state is drained by 34 river basins with about 54 major reservoirs and more than 300 medium and small anicuts, barrages, and diversion structures. Construction of dams, diversion structures, and barrages are centuries old. The Grand Anicut (called Kallanai in Tamil, kall = stone: Anai = dam) was constructed by the chola dynasty of King Karikalan during the second century BC. It is possibly the oldest existing structure on earth still in operation. At present, for convenience, the 34 river basins are grouped into 17 major river basins (Figure-2). Thus, almost 95 percent of the surface water potential is brought into human control by way of the construction of dams and anicuts. While major dams were constructed during British rule, medium projects were commissioned after independence. Most of the major rivers like Cauvery, Pennar, Palar are interstate rivers (Figure 2) and their flows in the state are dependent on certain mutual agreements with the neighboring states like Karnataka, Andhra Pradesh, and Kerala. Rivers are state subjects and therefore there are often disputes about sharing waters between the states. This problem is further aggravated when the political party in power in a state is different from the party that rules at the center. Moreover, since states have been divided on a linguistic basis, there are a number of reasons for disagreement.

Having utilized more than 90% of the available surface water resources, it is necessary for Tamil Nadu to develop its own groundwater resources, including a more judicious conjunctive use of its own surface and groundwater. The groundwater estimation committee (GWEC) constituted by the National Bank for Agriculture and Rural Development (NABARD) with the Central Ground Water Board (CGWB, 2000) and Groundwater wing of the public works department (PWD), estimated that the groundwater potential in Tamil Nadu is 22,432 Mm³, of which 1,022 Mm³ is earmarked for domestic and industrial water supply requirements (CGWB 2017). The actual requirement of water supply schemes is 1,057 Mm³ both for the urban and rural populations. However, these figures, although indicative of the overall water balance, should be taken with a great deal of caution, particularly as regards domestic water supply where spot-specific availability is as critical as sheer availability. At present, only 61% of the groundwater has been harnessed and it is still the most economical, individually managed (private) resource. Traditionally well irrigation was practiced in the eastern part of the state. There were open wells and the water was drawn by draught powered by bullocks. The depth and drawing of groundwater are directly related to the length and duration of travel by the bullocks, which helped in sustaining the groundwater without depriving groundwater from neighbors. The advent of electrification and use of high-powered pump sets, improvements in drilling technology, and the subsequent supply of free electricity for agricultural uses had led to the large-scale mining of groundwater, leading to dwindling quantities and deteriorating quality. It should be understood that the availability of an irreproachable standard constitutes part of the very quality of human life. The difficulties and cost of treating polluted water and the impossibility, even in the medium term, of rehabilitating polluted groundwater systems should encourage us to understand the vital need for maintaining good quality groundwater resources. The overexploitation of groundwater beyond the annual recharge into aquifers has already led to this resource being classified as exploited (CGWB 2017).

From the Table 1 it can be observed that 23 percent of total blocks experience heavy groundwater extraction, over and above the recharge, resulting in depletion and seawater ingress in the coastal aquifer system. By adapting spot-specific artificial groundwater recharge techniques continuously for more than a decade in Tamil Nadu, it is possible to recharge 3 and 4m thick sedimentary and hard rock terrains aquifers, respectively, and additionally, recharge about 375 TMC (Thousand Million Cubic feet) of groundwater.

India tops the list of countries with a large extent of the area brought under irrigation (total gross irrigated area of 62 MHA) (ICID, 2018). The state of Tamil Nadu with its limited resources ranks sixth in India and irrigates about 3.5 MHA (State of Indian Agriculture, 2016). By 2022 the total potential created under major and medium irrigation projects is reported at 1.34 MHA (90% of the assessed ultimate potential of 1.5 MHA) and minor irrigation potential of 2.20 MHA (91% of the ultimate potential of 2.4 MHA). The net sown area accounts for 42.6% of the total geographical area of which the net and gross irrigated areas as per the recent statistics were of the order of 2.4 and 2.9 MHA, respectively. It is estimated that rice crop consumes more than 45% of the total water that goes into agriculture. The major sources for irrigation are canals/rivers, tanks, and groundwater. The traditional utilization pattern of the water resources was one third each from reservoirs, tanks, and groundwater. Recently, the pattern transformed and the utilization at present is around 30 percent of reservoir water, 20 percent of tank water, and 50 percent of groundwater, respectively. Agriculture performance (Ruttan 1965; Gollin et al., 2002) is fundamental to India’s future economic and social development. Agriculture contributes 30% of GDP, 60% of employment, and is the primary source of livelihood in rural areas, which account for 75% of India’s population and 80% of its poor and low-income population. The performance of irrigated agriculture, which contributes 55% of agricultural output, will be the most important influence on these objectives. Therefore, the largest irrigated area in the world is in India (ICID, 2018).

There are 146 Municipalities and 15 Municipal Corporations in Tamil Nadu (Corporation of Tamil Nadu, 2020; Municipality of Tamil Nadu 2020). The metro water and the Tamil Nadu Water supply and Drainage Board (TWAD Board) are responsible for providing drinking water to the city of Chennai and the rest of the state, respectively. The drinking water requirement by the total population of Tamil Nadu by 2020 A.D is only 4.5% (1,055 Mm³ both for urban and rural population) of the total assessed groundwater resource, but every year the city of Chennai and most other towns face acute water scarcity (Vairavamoorthy et al., 2007). As the population has grown, freshwater (IPCC et al., 2014) has become increasingly less available where and when it is needed. Acute water shortages already have required extraordinary measures in Chennai, where water was transported from neighboring places by all modes of transport ranging from bicycles and trucks to railway tankers, with distances ranging from a few kilometers to 200 km. In certain parts of the city, people are forced to pay water tax and water charges to the government and at the same time, make daily purchases of drinking water from private vendors for drinking purposes.

The population of Tamil Nadu as per the 2011 census is 72.1 million (Census of India 2011) and the total population is expected to reach 85 million in the year 2021AD, out of which 32 million comprise the urban population and 53 million comprise the rural population (Figure 5). On a happy note, the substantial decline in the birth rate could fall further during the coming years. It was 28 per 1,000 during 2012 and 19.2 in 2022 and is expected to reach 15 per 1,000 during the year 2032. The water demand and supply projections have been made for agriculture, domestic, industrial and livestock requirements basin wise (as it would be an appropriate unit for planning any water resources system). For agriculture demand the cropping pattern, area sown, and water requirements are taken into account. For domestic purposes, the existing population in urban areas with a supply of 90 L per capita per day (lpcd) and rural with a supply of 40 L per capita per day has been taken (National Water Mission 2017). For industrial consumption, the yardstick fixed by the industries department is taken into account and for the livestock the number of cattle on each river basin is taken and an average consumption of 80 L per capita per day per cattle. The projection for future requirements for agriculture is made based on future schemes to be implemented in the river basins. For the assessment of domestic water supply, the population projections have been made for urban and rural areas. For urban areas, a 30 years 100% increase is taken. For rural areas, 30% was taken. For industrial projections, the annual increase of 8% was taken into consideration. As far as the livestock are concerned no norms for the increase have been fixed and as per the present requirement are taken for the projection also. From research studies, it was revealed that water needs during 2025 for irrigation, domestic, livestock, and industrial sectors are 55.28, 2, 1, and 2.5 billion m³, respectively.

Normally, dual-management irrigation systems are developed in a top-down approach. The water users in their “tertiary units” have to follow the technical and institutional innovations made by technicians. Recent rehabilitation programs have not improved irrigation as expected, and water users have not yet become “partners in irrigation management”. Good irrigation management appears to be difficult, as conflicting interests are normal in irrigation, and different parties have their own responsibilities.

Management strategies must be multifaceted rather than unimodel. It should have macro, micro, and grassroots level planning followed by effective management of catchment (on the upstream side) reservoir and the command (downstream side). The illegal felling of trees and excessive grazing over the catchment besides increasing runoff brings in silt and sediment which ends in surpluses to sea. Optimal catchment treatment would help in a great way in the proper upkeep of the structures created.

The experience in many developing countries has shown that the “fragmented, command-and-control” approach to the management of water resources has failed, both economically and environmentally. Hence, there is a need to use economic incentives and fiscal instruments in achieving economic efficiency in the use of the resource. Furthermore, it is necessary to show that better economic management of this resource will greatly assist in improving the environment. Thus, a policy package is urgently required with a judicious mix of legislation and regulation, including water tariffs, pollution taxes, effluent charges, and groundwater extraction charges, and providing tax benefits or investment support for water conservation and effluent treatment plants.

Surface water is utilized by scientific methods to the extent possible. Even then, the entire surface water available as surplus is not effectively and economically used, the surplus water (Suresh and Somasundaram, 1996; Suresh 2002) flows into the sea. The T.S. Vijaya Raghavan Committee (The Hindu, 2014) has estimated that from the seven river basins (Figure 2) of Tamil Nadu State, about 76.94 TMC of floodwater is let into the Bay of Bengal in the normal monsoon years. (Figure 6).

To improve the groundwater potential and quality it has been suggested that check dams be constructed across the rivers or surplus waters that could enable water to be diverted to areas in need, where the groundwater table is lower than the sea level. Traditional water management techniques have been neglected or fallen into disuse and are heading to a further decline in water storage capacity and consequently surface water flow into the sea. At present, the coordination between user departments is not up to the required level. The available water sources may be grouped for a river basin and various activities may be monitored. Nothing appreciable is being done to economize water use at present. The difficulties encountered in protecting the installed capacities and loopholes in the system. Tampering by the public, unwillingness to pay for water supply, insufficient qualified staff, paucity of funds, and delegation of powers at various levels may be considered conducive to the present reality.

Although improving the efficiency of existing irrigation schemes is a must, it is still not sufficient to meet the additional requirement for food and fiber in the next 2 decades. Large-scale new investments in irrigation schemes will be required for providing adequate food and fiber to meet the objectives of poverty alleviation and development. During the last decade, real investment in irrigation schemes has declined as the cost of new schemes has increased, while the international price of food grains has declined. Given the large contributions required from new schemes, concerted efforts are needed, both at national and international levels, to increase real investments in new irrigation schemes. Many of the delays in the completion of water resource projects often become costly and by the time a revised estimate is sanctioned another price escalation has already taken place.

The prestigious Water Resources Consolidation Project was carried out at an estimated cost of Rs.1400 crores for remedying the situation. Its main focus is on institutional arrangements, operation and maintenance, planning and management of farmer’s participation in water conservation and management, and environmental impact assessment. This project was also undertaken as part of a major revamping of the organizational structure of the Public Works Department (PWD).

An analysis of data reveals that fluoride, nitrate, iron, and Total Dissolved Solids (TDS) are the critical chemical parameters that noticeably influence water quality (Sivasankar et al., 2012). The Tamil Nadu districts of Dharmapuri, Salem, and Periyar are severely affected by fluoride. The districts of Coimbatore, Madurai, Virudhunagar, and Tuticorin are also affected to some level. In Dharmapuri District about 54% of the sources are found to be not potable either in one season or another season. High seasonal variation renders the same water sources as potable in one season and not potable in another season. Approximately 10% of the sources in Dharmapuri, Salem, and Erode have high fluoride levels of greater than 3 mg/L. Special attention is needed in these districts to avoid the problem of skeletal flourish. Cases of skeletal flourish have already been reported in Salem District. The level of Nitrate in most of the groundwater sources is becoming a problem and it has been noted in most of the districts. In the northwestern parts of Tamilnadu, it is above 60%. Increased agriculture activities and the application of fertilizers may be attributed to this phenomenon. Parts of the northern districts are affected by the high level of iron in the water. It has been observed that the iron content in any source generally decreases with continuous use.

High seasonal variation is noted in the level of TDS in groundwater sources in Tamilnadu. In Coimbatore about 90% of the water sources become non-potable for no specific season. With respect to groundwater sources, it is difficult to separately demarcate the saline areas in the state. The level of TDS depends on the water level and the depth of the well in various places. Certain pockets in the districts of Ramanathapuram (Sivasankar et al., 2012), Tuticorin, Pudukottai, and Coimbatore have a TDS of more than 3,000 mg/L. In these areas where water quality is a limiting factor, a change of source or treatment of water to bring it into a form suited for drinking purposes is required. Rainwater harvesting on rooftops and construction of percolation ponds (Figure 8) would result in diluting the groundwater by direct recharge and thus result in the portability of water.

In Tamil Nadu, there are about 4,820 highly polluting industries, which are called RED category industries. It has also been reported that out of the 5,059 industries listed as requiring effluent treatment plants, only 1,114 industries have provided the same type of effluent treatment plant. The impact of tannery pollution in the Palar river basin is in alarming proportion. The tannery effluent having high BOD, Sodium chloride, and chromium are let into the Palar river which takes water from infiltration wells is having high TDS, contrary to the expected quality for subsurface water in the river bed. High salinity is also noted in open well and bore well sources in Vaniyabadi, Ambur, Ranipet, Wallajah, and other towns in Tiruvannamalai, Vellore, Ranipet, and Tirupathur district. Dindigul is another district, which is severely affected by tannery pollution. Due to the depletion of present water sources and lowering of water levels in many of the bore wells, it is noted that the groundwater quality is severely affected. It is natural that when the groundwater level decreases the traveling time and contact time of water through soil increases and thus carries more salt with it.